JP2003262812A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a new optical scanner of a type that a plurality of surfaces to be scanned are simultaneously optically scanned with beams radiated from a plurality of light sources, and a part of an optical system forming an optical path leading to each surface to be scanned from the light source is made common. <P>SOLUTION: In the optical scanner, the several groups of beams are deflected by the same light deflection means and guided to the surface to be scanned different from every group of the beams by a scanning image-formation optical system so as to optically scan the several surfaces to be scanned. The respective groups of the beams deflected by the light deflection means 5 are transmitted through two scanning lenses. The scanning lens 7 out of the two scanning lenses transmits the several groups of beams going toward the different surfaces to be scanned, and its power in a main scanning direction: Pm and its power in a subscanning direction: Ps satisfy a condition: Pm>0≥Ps, and the scanning lenses 8A to 8D have positive power in the subscanning direction and transmit only the group of the beams going toward the same surface to be scanned. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and an image forming apparatus.

[0002]

2. Description of the Related Art A light beam from a light source side is deflected by a "light deflecting means" such as a rotating polygon mirror, and the deflected light beam is condensed toward a surface to be scanned by a "scanning image forming optical system" such as an fθ lens. To form a light spot on the surface to be scanned,
An optical scanning device that optically scans a surface to be scanned with this light spot is widely known in connection with image forming devices such as an optical printer, an optical plotter, a digital copying machine, and a facsimile device.

In recent years, not only optical scanning devices that optically scan a single surface to be scanned but also optical scanning devices that simultaneously optically scan a plurality of surfaces to be scanned have been put into practical use. In order to do so, "a part of an optical system that forms an optical path from a light source to each surface to be scanned is made common" (for example, Japanese Patent Laid-Open Nos. 2001-4948 and 2001). -10107, JP 2001-337A.
No. 20, JP 2001-343603 A, etc.).

[0004]

SUMMARY OF THE INVENTION The present invention is directed to an optical system that simultaneously optically scans a plurality of scanned surfaces with light beams emitted from a plurality of light sources and forms an optical path from the light source to each of the scanned surfaces. It is an object to realize a new optical scanning device of a partly common type.

Another object of the present invention is to realize a novel optical scanning device suitable for optically scanning a single surface to be scanned. Another object of the present invention is to realize a novel image forming apparatus using the above optical scanning device.

[0006]

According to another aspect of the present invention, there is provided an optical scanning apparatus, wherein: "a plurality of groups of light beams emitted from a plurality of light sources are deflected by the same light deflecting means, and a scanning image forming optical system is used for each group of light beams. An optical scanning device that guides light to different scanned surfaces and optically scans a plurality of scanned surfaces, and has the following features.

That is, each group of light beams deflected by the light deflecting means passes through at least two scanning lenses while being guided to the corresponding surface to be scanned. Among these scanning lenses, the scanning lens arranged at the position closest to the light deflecting means transmits a plurality of groups of light beams directed to different surfaces to be scanned, and has a power in the main scanning direction: Pm and a sub scanning direction. Power: Ps satisfies the condition: Pm> 0 ≧ Ps (condition: 1).

Further, the scanning lens arranged at the position closest to the surface to be scanned has a positive power in the sub-scanning direction and transmits only a group of light beams directed to the same surface to be scanned.

The "scanning lens arranged at the position closest to the light deflecting means" in the optical scanning device according to claim 1 has a radius of curvature of the incident side surface in the sub-scanning direction: Rs1, and an exit side surface in the sub-scanning direction. The radius of curvature: Rs2 together with the optical path length L from the starting point of the deflection of the light deflecting means to the surface to be scanned: condition: | (1 / Rs1) + (1 / Rs2) | .L <0.5 (condition: 2 ) Is satisfied (Claim 2).

The "scanning lens arranged at the position closest to the surface to be scanned" in the optical scanning device according to claim 1 or 2 has a radius of curvature in the main scanning direction of the incident side surface: Rm.
1. The radius of curvature of the exit side surface in the main scanning direction: Rm2 together with the optical path length from the origin of the deflection of the optical deflecting means to the surface to be scanned: L: | (1 / Rm1) + (1 / Rm2) | It is preferable that L <0.1 (condition: 3) is satisfied (claim 3).

An optical scanning device according to a fourth aspect is the optical scanning device according to any one of the first to third aspects, wherein the "plurality of light fluxes deflected by the optical deflecting means" are "optical deflecting means side. A scanning lens which has a positive power only in the main scanning direction and transmits a plurality of light fluxes guided to different scanned surfaces, and "a scanning lens disposed on the scanned surface side in the sub-scanning direction". And a scanning lens which has a positive power and transmits a group of light beams directed to the same surface to be scanned, and is guided to the surface to be scanned by only two scanning lenses.

In the optical scanning device according to any one of claims 1 to 4, the "scanning lens arranged at the position closest to the optical deflector" has no power in the sub-scanning direction. It is preferable that the “scanning lens arranged at the position closest to the surface to be scanned” has a thickness in the optical axis direction substantially within the effective region (lens region in the main scanning direction corresponding to the effective light scanning region in optical scanning). It is preferable that it is constant, and further, "the conjugate lateral magnification in the sub-scanning direction between the deflection starting point of the light deflecting means and the surface to be scanned: β" satisfies the condition: | β | <1.2 (condition: 4) It is preferable to be satisfied.

According to another aspect of the optical scanning device of the present invention, "a plurality of groups of light beams emitted from a plurality of light sources are deflected by the same light deflecting means, and a scanning image forming optical system forms a different surface to be scanned for each light beam group. An optical scanning device that guides light and optically scans a plurality of surfaces to be scanned ", and has the following features.

That is, a scanning and imaging optical system for guiding each group of light beams deflected by the light deflecting means to the surface to be scanned is as follows.
Type scanning lens. The first type of scanning lens has a plurality of groups of light beams directed to different surfaces to be scanned, in which the power Pm in the main scanning direction and the power Ps in the sub scanning direction satisfy the condition Pm> 0 ≧ Ps (condition: 1). Through.

The second type scanning lens has a positive power in the sub-scanning direction and transmits a group of light beams directed to the same surface to be scanned. Then, all the scanning lenses arranged on the optical path from the light deflecting means to each surface to be scanned are either the first type or the second type of scanning lenses. For example, when the scanning imaging optical system has three scanning lenses, one of them is a first type scanning lens, the other one is a second type scanning lens, and the remaining one is a first or second scanning lens. It is a second type of scanning lens.

In the optical scanning device according to claim 5, "first
In the scanning lens of the type, the radius of curvature of the incident side surface in the sub-scanning direction: Rs1 and the radius of curvature of the exit side surface in the sub-scanning direction: Rs2 are the optical path lengths from the origin of deflection of the light deflecting means to the scanned surface: It is preferable to satisfy the condition: | (1 / Rs1) + (1 / Rs2) | L <0.5 (condition: 2) together with L (claim 6).

In the "second type scanning lens" in the optical scanning device according to the fifth or sixth aspect, the entrance side surface has a radius of curvature Rm1 in the main scanning direction and the exit side surface has a radius of curvature Rm2 in the main scanning direction. , The optical path length from the deflection origin of the light deflecting means to the surface to be scanned: L, and the condition: | (1 / Rm1) + (1 / Rm2) | .L <0.1 (condition: 3) Is preferred (Claim 7).

In the optical scanning device according to any one of claims 5 to 7, it is preferable that the "first type scanning lens" has no power in the sub-scanning direction, and "the closest to the surface to be scanned". It is preferable that the "scanning lens disposed at a position" has a substantially constant thickness in the optical axis direction within the effective area,
It is preferable that the conjugate lateral magnification: β in the sub-scanning direction between the deflection starting point of the light deflecting means and the surface to be scanned satisfies the condition: | β | <1.2 (condition: 4).

Further, the scanning image forming optical system in the optical scanning device according to any one of claims 5 to 7 includes one scanning lens of the first type and one scanning lens of the second type. It can be configured as the two-sheet configuration used.

In the optical scanning device according to any one of claims 1 to 7, "out of a plurality of groups of light beams deflected by the light deflecting means, at least two groups of light beams are substantially parallel to the sub-scanning direction. It is preferable.

An optical scanning device according to an eighth aspect of the present invention is an optical scanning device in which "a single group of light beams emitted from a light source are deflected by an optical deflecting means and guided by a scanning imaging optical system to a surface to be scanned for optical scanning. The device is characterized by the following points.

That is, the scanning imaging optical system is composed of two scanning lenses. Of these two scanning lenses, the scanning lens on the side of the optical deflector is a lens having power only in the main scanning direction. In the scanning lens on the surface to be scanned, the radius of curvature of the entrance side surface in the main scanning direction: Rm1 and the radius of curvature of the exit side surface in the main scanning direction: Rm2 are from the origin of deflection of the light deflecting means to the surface to be scanned. The optical path length: L, and the condition: | (1 / Rm1) + (1 / Rm2) | .L <0.1 (condition: 3) are satisfied. It is preferable that the “scanning lens disposed on the surface to be scanned” in the optical scanning device according to claim 8 has a substantially constant thickness in the optical axis direction within the effective region.

A slight supplement will be given. In the above description, the “light flux group” refers to the total number of light fluxes used for optically scanning a certain surface to be scanned. If the surface to be scanned is optically scanned by the single-beam scanning method, the "flux group" in this case
Is composed of "one light beam". When the surface to be scanned is optically scanned by the multi-beam scanning method, a plurality of light beams that simultaneously scan the surface to be scanned by multi-beam form a “light flux group”.

Therefore, the optical scanning of the surface to be scanned in the optical scanning device of the present invention can be either a "single beam scanning system" or a "multi-beam scanning system".

In the optical scanning device according to any one of claims 1 to 7, since there are "a plurality of light sources" and there is a surface to be scanned equal to the number of light sources, a group of luminous flux is emitted from each light source. 1
The light flux of the group (the above-mentioned “group of light fluxes”) optically scans the surface to be scanned corresponding to the light source.

Therefore, "a plurality of light fluxes" are emitted from the plurality of light sources as a whole, and the plurality of light fluxes are deflected by the same light deflecting means. Examples of the “light deflecting means” include a rotating polygon mirror that rotates a polygon mirror, a rotating one-sided mirror and a rotating two-sided mirror such as a pyramidal mirror and a hoso-type mirror.
Alternatively, various conventionally known ones such as a galvanometer mirror can be used. As the "same optical scanning means", "a means for coaxially integrating a plurality of polygons and integrally rotating them" can be used as will be described later.

Further, in the optical scanning device according to any one of claims 1 to 7, the plurality of groups of light beams optically scan the surface to be scanned different from each other. In this case, the "surfaces to be scanned different from each other" are: For example, "when the areas to be optically scanned differ greatly" on the same drum-shaped or belt-shaped photosensitive member is also included in the category. That is, in such a case, even if the surfaces to be scanned are different from each other, the photoconductors that are the entities of these surfaces to be scanned are the same.

The image forming apparatus according to the present invention "in an image forming apparatus for forming an image by optically scanning one or more photosensitive mediums, the optical scanning apparatus according to any one of claims 1 to 8 is used." It is characterized by (claim 9).

Various types of "photosensitive medium" are possible. For example, a "silver salt film" can be used as the photosensitive medium. In this case, a latent image is formed by writing by optical scanning, and this latent image can be visualized by processing by a normal silver salt photographic process. Such an image forming apparatus can be implemented as an "optical plate making apparatus" or an "optical drawing apparatus" for drawing a CT scan image or the like.

As the photosensitive medium, it is also possible to use a "coloring medium which develops color by the thermal energy of a light spot during optical scanning". In this case, a visible image can be directly formed by optical scanning.

As the photosensitive medium, a "photoconductive photoreceptor" can be used. As the photoconductive photoconductor, a sheet-like one such as zinc oxide paper can be used, or a selenium photoconductor, an organic photo-semiconductor or the like "a drum-shaped or belt-shaped repeatedly used one" can be used. You can

When a photoconductive photoconductor is used as a photosensitive medium, an electrostatic latent image is formed by uniformly charging the photoconductor and optical scanning with an optical scanning device. The electrostatic latent image is visualized as a toner image by development. The toner image is directly fixed on the photosensitive medium when the photosensitive medium is in the form of a sheet such as zinc oxide paper, and when the photosensitive medium is reusable, transfer paper or OHP sheet is used. It is transferred and fixed on a sheet-shaped recording medium such as (plastic sheet for overhead projector).

The transfer of the toner image from the photoconductive photoconductor to the sheet-shaped recording medium may be carried out directly from the photoconductor to the sheet-shaped recording medium (direct transfer method), or once the intermediate image is transferred from the photoconductor. After transferring to an intermediate transfer medium such as a transfer belt,
You may make it transfer from this intermediate transfer medium to a sheet-shaped recording medium (intermediate transfer system). Such an image forming apparatus can be implemented as an optical printer, an optical plotter, a digital copying machine, or the like.

As an optical scanning device, a system for optically scanning a plurality of scanned surfaces with light beams from a plurality of light sources (the above-mentioned claim 1
In the case of the image forming apparatus using any of (7) to (7), "3 or 4 photoconductive photoconductors" forming the substance of the surface to be scanned by the light flux from each light source are arranged in parallel with each other, It can be implemented as a well-known "tandem type color image forming apparatus".

It is also possible to use an "imaging mirror" for the imaging element "arranged closest to the surface to be scanned" in the scanning imaging optical system of the above optical scanning device. Since a means for separating the incident light flux and the reflected light flux is required, the layout of the optical system is tightly restricted, and the scanning line bends. Further, if the main scanning direction has no power, there is a problem that it is difficult to reduce the lateral magnification ratio in the sub-scanning direction. Therefore, it is preferable to use the scanning lens.

In the optical scanning device according to any one of claims 1 to 8,
In order to prevent ghost light, it is preferable that the incident side surface of the scanning lens arranged closest to the light deflecting means has a “convex shape toward the light deflecting means”. In the optical scanning device of the present invention, if the incident side surface of the scanning lens closest to the optical deflecting means has a "concave shape toward the optical deflecting means side", a part of the deflected light beam is reflected by this incident side surface and the optical deflection is performed. There is a possibility that the light returns to the means, is further reflected by the deflective reflection surface, is incident on the scanning lens again, and reaches the surface to be scanned as ghost light.

Since this scanning lens has no positive power in the sub-scanning direction, the incident side surface is likely to be a surface having no curvature or a concave shape in the sub-scanning direction, and the component reflected by the incident side surface returns to the light deflecting means. easy. When a plurality of groups of deflected light beams enter the scanning lens as in claims 1 to 7, this tendency is remarkable and ghost light is likely to be generated.

By making the incident side surface of the scanning lens closest to the light deflecting means "convex shape toward the light deflecting means", the light beam reflected by the incident side surface advances in the "direction away from the light deflecting means". As a result, it is possible to effectively reduce the influence of the east light on the surface to be scanned.

Further, by making the incident side surface "convex toward the light deflecting means", the positive power of this scanning lens can be effectively distributed to the incident side surface and the exit side surface. Therefore, aberration correction becomes easy.

It is preferable that the exit surface of the scanning lens arranged closest to the surface to be scanned be "curved in the main scanning direction". By curving in the main scanning direction in this way, it becomes easy to correct the scanning line curve. That is, the scanning line bending can be effectively corrected by rotationally adjusting the scanning lens around the "axis parallel to the main scanning direction".

Since the scanning lens closest to the optical deflector has a small power in the sub-scanning direction, the lateral magnification ratio in the sub-scanning direction depending on the image height is determined by "the scanning lens closest to the surface to be scanned". The lateral magnification in the sub-scanning direction here is the "lateral magnification in the sub-scanning direction between the deflective reflection surface and the surface to be scanned".

By curving the exit side (scanned surface side) lens surface of the scanning lens closest to the scanned surface in the main scanning direction, the lateral magnification ratio in the sub scanning direction due to the image height can be reduced,
The deviation between the image heights of the beam diameter (light spot diameter) in the sub-scanning direction and the deviation between the image heights of the scanning line pitch in the case of multi-beam scanning can be reduced.

In each embodiment described later, the image height-to-height ratio of the lateral magnification in the sub-scanning direction is set to 9% or less, but it is "optimized for the curved shape in the main scanning direction" of the scanning lens closest to the surface to be scanned. The image height ratio can be further reduced.

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a diagram for explaining one embodiment of the image forming apparatus. FIG. 1A shows the arrangement of the optical system after the polygon mirror 5 of the rotary polygon mirror which is the light deflecting means.

In this embodiment, the four groups of light beams emitted from the four light sources are deflected by the polygon mirror 5 which is the same light deflecting means. Each group of 4 groups of luminous flux is
As described above, when the optical scanning is performed by the multi-beam scanning method, each group may have a plurality of light beams, but here, for the sake of concreteness of the description, each of the four light beams has one light beam. It is assumed that Therefore, in the following description, the group of luminous fluxes will be simply referred to as “luminous flux”.

The four groups of luminous fluxes deflected by the polygon mirror 5 pass through the common first scanning lens 7 and are then respectively reflected by the optical path bending mirrors MA1, MA2, MB1, MB.
After being reflected by 2, MC1, MC2, MD1 and MD2, the second scanning lenses 8A, 8B, 8C and 8D are provided for each light beam.
And enters the photoconductive photoconductors 9A, 9B, 9C and 9D, which are photosensitive media forming the substance of the surface to be scanned, and form a light spot on the photoconductive surface.

Then, as the polygon mirror 5 rotates, each light spot is displaced on the corresponding photoconductor to perform optical scanning (main scanning). The photoconductors 9A to 9D rotate at a constant speed in the arrow direction. Sub-scanning is performed by this rotation of the photoconductor.

FIG. 1B is a developed view of the optical arrangement on the optical path from each light source to the corresponding surface to be scanned in the embodiment shown in FIG. 1A. The light beam emitted from the light source 1 is converted into a parallel light beam by the collimator 2,
The beam is “beam-shaped” by passing through the aperture 3, passes through a cylindrical lens 4 as a line image forming optical system, is focused only in the sub-scanning direction, and is a virtual mirror 6 (virtually for facilitating drawing). It is inserted in the optical path. It is actually unnecessary.) And is imaged at the position of the deflecting reflection surface of the polygon mirror 5 as a "line image long in the main scanning direction" separated from each other in the sub scanning direction.

Each light beam deflected by the rotation of the polygon mirror 5 passes through the common first scanning lens 7 and has its optical path bent by an optical path bending mirror (not shown in FIG. 1B). The light enters the photoconductors 9A to 9D through the second scanning lenses 8A to 8D.

As shown in FIG. 1D, the four light beams deflected by the polygon mirror 5 are substantially parallel to each other in the sub-scanning direction and are close to each other. In this way, since the four light beams deflected at the same time are close to each other in the sub-scanning direction, the "size in the rotation axis direction" of the deflective reflection surface of the polygon mirror 5 can be small, and the polygon mirror 5 can be made lightweight. Therefore, the polygon mirror 5 can be rotated at high speed with less energy.

Various methods are possible to make the four light beams deflected simultaneously by the polygon mirror 5 "parallel to each other in the sub-scanning direction and close to each other", but as an example, FIG. ) Can be mentioned.

That is, the four light sources 1A, 1B, 1C, 1D
Are four semiconductor laser emission sources in the semiconductor laser array. The four light beams emitted from these light sources 1A to 1D are converted into parallel light beams by the collimator lens 2 and condensed in the sub-scanning direction by the cylindrical lens 4, but the collimator lens 2 and the cylindrical lens 4 are arranged in the sub-scanning direction (see FIG. In (c) the up-down direction), an afocal system is formed so that the principal rays of the light flux emitted from the cylindrical lens 4 (condensed in the sub-scanning direction) are parallel to each other in the sub-scanning direction.

As a method of guiding a plurality of light fluxes substantially parallel to each other in the sub-scanning direction from the light source side to the light deflecting means, a synthetic prism may be used, or the light fluxes may be spread between the light fluxes in the main scanning direction when viewed from the sub-scanning direction. The method of giving a corner and using a folding mirror can be mentioned.

Returning to FIG. 1A, all of the four light beams deflected simultaneously by the polygon mirror 5 pass through the first scanning lens 7, and the first scanning lens 7 moves in the main scanning direction. Power: Pm and power in the sub-scanning direction: Ps
Satisfies the condition: Pm> 0 ≧ Ps (condition: 1). Further, the second scanning lenses 8A to 8D arranged on the scanned surfaces 9A to 9D side have positive power in the sub-scanning direction and transmit only the group of light beams directed to the same scanned surface.

That is, in the optical scanning device in the embodiment shown in FIG. 1, a plurality of groups of light beams emitted from a plurality of light sources 1A to 1D are deflected by the same optical deflecting means 5, and the scanning imaging optical system is used. Scanned surfaces 9A to 9 that are different for each group of light fluxes
An optical scanning device which guides light to D and optically scans a plurality of scanned surfaces 9A to 9D, wherein each group of light beams deflected by the optical deflecting means 5 is guided to the corresponding scanned surface. Of at least two scanning lenses, and among these scanning lenses, the scanning lens 7 arranged at the position closest to the light deflecting means transmits a plurality of groups of light beams directed to different scanned surfaces 9A to 9D. , Its power in the main scanning direction: Pm
And the power Ps in the sub-scanning direction satisfies the condition: Pm> 0 ≧ Ps (condition: 1), and the scanning lenses 8A to 8D arranged at the position closest to the surface to be scanned are arranged in the sub-scanning direction. It has a positive power and transmits only a group of light beams directed to the same surface to be scanned (Claim 1).

The meaning of the condition 1 that the first scanning lens 7 satisfies will be described. First, the significance of setting Ps ≦ 0 will be described. In FIG. 2A, reference numeral 5A denotes a deflecting / reflecting surface of the polygon mirror 5, and the figure shows a state in which the light flux is reflected from the origin of deflection toward the surface to be scanned. Code 7
Indicates a main surface of the first scanning lens in the sub-scanning direction, reference numeral 8 indicates a main surface of any one of the second scanning lenses 8A to 8B, and reference numeral 9 indicates a surface to be scanned.

As described with reference to FIG. 1, the light beams reflected by the deflective reflection surface 5A are parallel to each other in the sub-scanning direction and are close to each other. Separating a plurality of light beams that are close to each other in the sub-scanning direction into respective optical paths that reach the surface to be scanned, which is a major problem in such an optical system.

In order to facilitate such light beam separation, it is effective to "reduce the light beam width in the sub-scanning direction" and "increase the interval between different light beams in the sub-scanning direction". Considering the case where Ps = 0, Ps> 0, and Ps <0 as the power Ps of the first scanning lens 7 in the sub-scanning direction, when the solid line in FIG. 2A is Ps = 0,
The broken line corresponds to Ps <0 and the chain line corresponds to Ps> 0.

From this figure, by setting Ps ≦ 0,
It can be seen that “the light flux width in the sub-scanning direction can be reduced” as compared with the case of Ps> 0.

By the way, in recent years, high density
High image quality is required, and it is desired to reduce the diameter of the light spot on the surface to be scanned. The spot diameter of the light spot in the sub-scanning direction is determined by the angle shown in FIG. 2A: θ (convergence angle of the light beam toward the surface to be scanned in the sub-scanning direction).
Is larger, the spot diameter in the sub-scanning direction can be smaller.
That is, the convergence angle: θ for realizing the same spot diameter for light fluxes of the same wavelength is constant.

Conventionally, in the optical scanning device of the type shown in FIG. 1, the first scanning lens normally has "a positive power in the sub-scanning direction", but as shown in FIG. When the power Ps of the 1-scanning lens 7 in the sub-scanning direction becomes positive, the luminous flux width in the sub-scanning direction between the first and second scanning lenses (the luminous flux must be separated in this region) is shown by the chain line. It becomes large and the light beam separation becomes difficult.

When Ps = 0, since the first scanning lens 7 does not refract in the sub-scanning direction, the light beam width in the sub-scanning direction between the first and second scanning lenses can be reduced as shown by the solid line. Light beam separation becomes easy. When Ps <0, the luminous flux width in the sub-scanning direction between the first and second scanning lenses can be further reduced, and the luminous flux separation becomes easier. Even if the power Ps is set to Ps ≦ 0 in this way, the convergence angle: θ
By setting the arrangement position of the second scanning lens 8 and the power in the sub-scanning direction so as to give a necessary value to the light spot, it is possible to realize a light spot whose diameter is reduced in the sub-scanning direction.

In FIG. 2B, the principal rays (parallel to each other in the sub-scanning direction) of the two light beams reflected by the deflecting / reflecting surface 5A of the polygon mirror 5 are transmitted through the first scanning lens 7. It shows the situation. When the power Ps of the first scanning lens 7 in the sub-scanning direction is Ps = 0, as shown by the solid line, the luminous flux interval in the sub-scanning direction between the two luminous fluxes does not change even after passing through the lens.

When Ps <0, as shown by the broken line, the light flux interval is expanded in the sub-scanning direction after passing through the lens. Therefore, P
When s ≦ 0, light beam separation is easy. In contrast,
When Ps> 0, the distance between the two light beams after passing through the lens is narrowed in the sub-scanning direction as indicated by the chain line, and thus light beam separation becomes difficult.

According to the first aspect of the invention, the power of the scanning lens 7 arranged at the position closest to the light deflecting means: P
When m and the power in the sub-scanning direction: Ps satisfy the condition: Pm> 0 ≧ Ps (condition: 1), the scanning lens arranged at the position closest to the surface to be scanned naturally has “ It must have a positive power in the sub-scanning direction.

On the other hand, since there is no problem of light beam separation in the main scanning direction, the power of the scanning lens on the side of the light deflecting means:
Pm is set to Pm> 0. In this case, the positive power: Pm applied to the scanning lens closest to the light deflector is used to correct the "imaging characteristics (field curvature etc.) in the main scanning direction on the surface to be scanned and the constant velocity characteristics (fθ characteristic etc.). ) "Most of the correction function" can be imposed. In particular, when most of the constant velocity characteristic correction function is provided, the deflection angle of the deflected light beam becomes smaller than that of the scanning lens on the surface to be scanned. Therefore, the size of the scanning lens on the surface to be scanned (the second scanning lens 8 in the above example) in the main scanning direction can be reduced.

The optical scanning device described above with reference to FIGS. 1, 2A, and 2B also deflects a plurality of groups of light beams emitted from a plurality of light sources by the same light deflecting means 5. Then, the surface 9A to be scanned which is different for each light flux group by the scanning and imaging optical system.
9D to 9D to optically scan a plurality of scanned surfaces 9A to 9D, which is a scanning imaging optical system that guides each group of light beams deflected by the optical deflecting means to the scanned surface. But the first
This type of scanning lens 7 and second type scanning lenses 8A to 8D.

In the first type scanning lens 7, the power in the main scanning direction: Pm and the power in the sub-scanning direction: Ps satisfy the condition Pm> 0 ≧ Ps (condition: 1), and the scanning lens 7 faces a different surface to be scanned. Transmits multiple groups of light flux.

The second type scanning lenses 8A to 8D are
It has a positive power in the sub-scanning direction and transmits a group of luminous fluxes directed to the same surface to be scanned. Then, all the scanning lenses arranged on the optical path from the light deflecting means 5 to the respective scanned surfaces 9A to 9D are either the first type or the second type scanning lenses. Therefore, the optical scanning device of FIG.
This is one embodiment of the optical scanning device described.

As described above, the scanning lens on the side of the light deflection means
Positive power applied to the (first type): Pm has a large function of correcting the image forming characteristic (field curvature etc.) in the main scanning direction on the surface to be scanned and the constant velocity characteristic correction (fθ characteristic etc.). Although it is possible to occupy a portion, this lens transmits a plurality of light beams directed to different scanned surfaces, so that the constant velocity characteristic correction function is common to the light beams directed to each scanned surface. Therefore, “relative optical scanning position deviation in the main scanning direction on different scanned surfaces (which causes color deviation in the main scanning direction in the case of color image formation)” due to processing variations and temperature distribution of the scanning lens The number of lenses and the number of parts for holding the lenses can be reduced by using a common lens for a plurality of light beams.

Further, by satisfying the condition of Ps ≦ 0, it becomes easy to separate the light beams from each other. Therefore, the "axial dimension" of the deflecting / reflecting surface of the light deflecting means can be small, and the light deflecting means can be downsized, low in power consumption, high in durability, and low in noise. Further, the scanning lens close to the light deflector can be downsized.

Further, by giving a positive power in the sub-scanning direction to the "scanning surface side scanning lens" through which only the light beam traveling to the same scanning surface is transmitted, the scanning line bending can be reduced.

Further, a first type scanning lens (having a positive power: Pm in the main scanning direction) which transmits a plurality of light beams directed to different scanned surfaces, and a type which transmits only a light beam directed to the same scanned surface 2 (having a positive power in the sub-scanning direction) can be completely functionally separated,
By utilizing this function separation, it is possible to reduce the difference in constant velocity characteristics and scanning line bending on different scanned surfaces, and to reduce the relative displacement of the optical scanning position on each scanned surface in the main and sub-scanning directions. It is possible to realize a small number of optical scanning devices.

Next, the condition: 2 (claims 2 and 6) will be described. As in the optical scanning device according to any one of claims 1 and 5, "a plurality of groups of light beams emitted from a plurality of light sources are deflected by the same light deflecting means 5 and different surfaces to be scanned by the scanning and imaging optical system. In the case of an "optical scanning device that guides light to and optically scans multiple scanned surfaces," the images written on each scanned surface are aligned and superimposed on each other to form a color image or a multicolor image. It is common to be done.

In such a case, if there is a "relative positional deviation of the scanning position in the main / sub scanning direction" between the surfaces to be scanned, a phenomenon called "color misregistration" appears in the formed color image and the image quality is improved. Is well known, and therefore, in the optical scanning device as described above, it is an important issue to reduce "relative displacement of the optical scanning position on different scan surfaces". Condition: 2 parameters: | (1 / Rs1) +
If the value of (1 / Rs2) | L exceeds the upper limit value of 0.5, the following problems occur.

As described above, the scanning lens on the side of the optical deflector has a power Ps in the sub-scanning direction of Ps ≦ 0. However, when the absolute value of the power Ps becomes large, a plurality of light fluxes passing through this scanning lens The shape in the main scanning direction differs depending on the “transmission position in the sub scanning direction”. Therefore, in the case where "a large part of the constant velocity characteristic correction function" is given to this scanning lens, a difference occurs in the constant velocity characteristic due to the light beam, and the relative main scanning direction on different scanned surfaces is changed. The scanning position shift becomes large.

The power of the scanning lens in the sub-scanning direction:
If the absolute value of Ps is large, a difference occurs in the scanning line bending characteristics between the light beams, and the relative optical scanning misalignment in the sub-scanning direction on different scan surfaces increases. By satisfying the condition: 2, it is possible to reduce the relative optical scanning position deviation in the main and sub scanning directions on different scan surfaces.

Next, the meaning of condition 3 (claims 3 and 7) will be described. As described above, since the scanning lens closest to the optical deflector and the scanning lens of the first type "transmit a plurality of light beams traveling to different surfaces to be scanned", the function of correcting the constant velocity characteristic is as much as possible for this scanning lens. It is good to have
It is better not to impose the "constant velocity characteristic correction function" on the scan lens on the scan surface side or the second type scan lens that transmits only the light beam traveling to the same scan surface.

Condition: 3 parameters | (1 / Rm1) +
When (1 / Rm2) | · L exceeds the upper limit value of 0.1, the difference in shape of the scanning lens closest to the surface to be scanned and the second type scanning lens due to variations in processing and the temperature difference between the lenses. Due to the difference in the shape and the refractive index caused by the difference in the uniform velocity characteristics between the different surfaces to be scanned, the relative deviation of the optical scanning position in the main scanning direction between the surfaces to be scanned becomes large.

If Condition 3: is satisfied, the shape difference and the refraction of the scanning lens closest to the surface to be scanned and the second type scanning lens due to variations in processing, and the shape and refraction due to the temperature difference between the respective lenses. Even if there is a difference in the ratio, since the contribution to the constant velocity characteristic of the scanning lens is small, it is possible to reduce the relative deviation of the optical scanning position in the main scanning direction between the surfaces to be scanned.

As described above, the "scanning lens arranged closest to the light deflector" and the "first type scanning lens" have no power in the sub-scanning direction. It is preferable that the "scanning lens disposed at the position closest to the surface to be scanned" has a substantially constant thickness in the optical axis direction within the effective area, and further, " Conjugate lateral magnification in the sub-scanning direction between the surfaces to be scanned: β "
However, it is preferable to satisfy the condition: | β | <1.2 (condition: 4).

If the scanning lens closest to the optical deflector or the scanning lens of the first type has no power in the sub-scanning direction and Ps = 0, "on a different surface to be scanned" due to the scanning lens. Relative scan position deviation in the sub-scan direction ”
Can be set to 0, and the scanning line bending itself can be reduced.

If the scanning lens arranged closest to the surface to be scanned and the scanning lens of the second type have a "substantially constant thickness in the optical axis direction within the effective area", Since the scanning lens does not have a constant velocity characteristic correction function, even if a difference in shape or a difference in refractive index due to a difference in processing of the lens or a temperature difference between the lenses occurs, relative scanning on different surfaces to be scanned occurs. It is possible to reduce the "scan position in the main scanning direction".

Condition: The significance of 4 will be described. In FIG. 2C, reference numeral 5A indicates a deflective reflection surface, reference numeral 9 indicates a surface to be scanned, and reference numeral 7 indicates a scanning lens on the side of the optical deflector. Also, reference numeral 8
Reference numerals 0 and 81 denote two kinds of scanning lenses on the surface to be scanned, but the scanning lens 80 has a large conjugate lateral magnification: β in the sub-scanning direction,
The scanning lens 81 has the same magnification: β is small. As described above, the spot diameter in the sub-scanning direction is determined by the convergence angle: θ in the sub-scanning direction of the light beam traveling toward the surface 9 to be scanned. The larger the convergence angle: θ, the smaller the diameter of the light spot. Figure 2
The solid line in (c) shows the light beam width in the sub-scanning direction when | β | is small, and the broken line shows the light beam width in the sub-scanning direction when | β | is large. Both have the same convergence angle: θ, and can realize the same spot diameter in the sub-scanning direction, but when | β | is large, the luminous flux width is large, and |
When β | is small, the luminous flux width is small.

Particularly, when | β | becomes 1.2 or more, the luminous flux width becomes very large, and it becomes difficult to separate the luminous flux. In this case, in order to enable the light beam separation, the distance between the light beams on the deflective reflection surface 5 must be increased in the sub-scanning direction.
This inevitably leads to an increase in the size of the light deflecting means.

If | β | <1.2 is satisfied, the light beam separation is easy, and the size of the light deflector is not increased.
It is possible to realize low power consumption, high durability, and low noise. Further, the scanning lens closest to the light deflector can be downsized.

In the above-described embodiment, a plurality of groups of light beams deflected by the light deflecting means are arranged on the light deflecting means side and have a positive power in the main scanning direction, so that they are formed on different scanned surfaces. Scanning lens 7 that transmits a plurality of light fluxes that are guided
And the scanning lenses 8A to 8D which are disposed on the surface to be scanned side and have a positive power in the sub-scanning direction and which transmit a group of light beams directed to the same surface to be scanned. The light is guided to 9A to 9D.

In this case, the scanning lens 7 can be made to have "positive power only in the main scanning direction and no power in the sub scanning direction (Ps = 0)" (claim 4).

In this way, the number of scanning lenses can be small even when a plurality of surfaces to be scanned are optically scanned. For example, as in the case of the embodiment shown in FIG. 1, even if there are four different scanned surfaces 9A to 9D, a total of five scanning lenses (scanning lenses 7, 8A to 8D) will suffice. On the other hand, if independent scanning and imaging optical systems are used for each surface to be scanned and each requires two lenses, eight lenses are required.

Further, if the scanning lens 7 on the side of the optical deflector is set so as not to have power in the sub-scanning direction, the relative scanning position shift in the sub-scanning direction between the surfaces to be scanned due to the scanning lens 7 is caused. Can be set to 0 and the scan line bend can be set to 0,
It is possible to reduce the relative deviation of the scanning position in the sub-scanning direction between the surfaces to be scanned.

Further, when the number of scanning lenses through which the deflected light beam is transmitted is only two, that is, the first and second types, the number of lens-related parts can be reduced and the degree of freedom of layout can be improved as the number of lenses is reduced. However, it becomes possible to realize a small optical scanning device.

As described above, it is preferable that at least two groups of light beams among the plurality of groups of light beams deflected by the light deflecting means are “substantially parallel to the sub-scanning direction”. By doing so, it is possible to reduce the relative difference in the scanning line curve between the surfaces to be scanned.

In the embodiment shown in FIG. 1, the scanning imaging optical system for each surface to be scanned is composed of the scanning lens 7 and one of the scanning lenses 8A to 8D. Each of the image optical systems is a scanning device used in "an optical scanning device that performs optical scanning by deflecting a single group of light beams emitted from a light source by a light deflecting means and guiding the light to a surface to be scanned by a scanning imaging optical system". It can also be used as an image optical system (claim 8).

That is, the scanning image forming optical system used in the optical scanning device of claim 8 is composed of two scanning lenses, and the scanning lens on the side of the optical deflector is a lens having power only in the main scanning direction. The radius of curvature Rm1 of the incident side surface of the scanning lens on the scanning surface side in the main scanning direction and the radius of curvature Rm2 of the exit side surface in the main scanning direction together with the optical path length L from the origin of deflection of the light deflecting means to the surface to be scanned: L , Condition: | (1 / Rm1) + (1 / Rm2) | L <0.1 (Condition: 3) is satisfied.

Conditions for the scanning lens on the side closer to the surface to be scanned: 3
If the above condition is satisfied, most of the function of correcting the constant velocity characteristic can be assigned to the scanning lens on the side closer to the light deflector. Since the power of the scanning lens on the side of the optical deflector is 0 in the sub-scanning direction, even if the light beam incident on the scanning lens on the side closer to the optical deflector is displaced in the sub-scanning direction, the main scanning cross section (the optical axis There is no shape change in a virtual cross section parallel to the main scanning direction), constant velocity characteristics do not deteriorate, and imaging performance in the main scanning direction does not deteriorate.

Even if there is a local defect such as a foreign substance in the scanning lens near the light deflector, since there is no optical axis in the sub-scanning direction, the best sub-scanning position is selected and the scanning lens is selected. Can be deployed.

Also in this case, the scanning lens arranged at the position closest to the surface to be scanned is set so that the thickness in the optical axis direction is substantially constant in the effective area, so that the side closer to the light deflecting means. Even if the light beam incident on the scanning lens shifts in the sub-scanning direction, there is no change in shape in the main-scanning cross section, no deterioration in constant velocity characteristics, and no deterioration in imaging performance in the main-scanning direction.

Another embodiment of the image forming apparatus is shown in FIG. A sheet feeding cassette 10 is arranged in the lower part of the apparatus, and a conveying belt 12 that conveys a transfer sheet S, which is a sheet-shaped recording medium fed from the sheet feeding cassette 10, is provided above the sheet feeding cassette 10. Four photosensitive media 13 are provided on the conveyor belt 12.
Y, 13M, 13C and 13K are conveyor belts 12 as shown in the figure.
Are arranged along the circumference of.

In the following description, Y, M, C and K are associated with yellow, magenta, cyan and black, respectively. The photosensitive media 13Y, 13M, 13C, and 13K are all photoconductive photoconductors, and will be referred to as “photoconductors 13Y to 1Y” below.
3K ”.

The photoconductors 13Y to 13K are formed to have the same diameter, and process means according to the image forming process are sequentially arranged around each photoconductor. Taking the photoconductor 13Y as an example, the charging unit 4Y, the developing device 5Y, and the transfer charger 6
Y, a cleaning device 7Y and the like are provided.

The photoconductors 13Y to 13K are arranged at equal intervals from the upstream side to the downstream side of the transfer sheet S conveying path, that is, from the right side to the left side in the drawing. Conveyor belt 12
Of the registration roller 19 on the upstream side of the photoconductor 5Y.
A charger 20 is provided, and a separating unit 21, a charge eliminating unit 22, and a belt cleaner 23 are provided on the downstream side of the photoconductor 5K. A fixing device 24 is provided on the downstream side of the transfer paper transport path of the separating means 21. A discharge roller 25 is provided at the end of the transfer paper transport path, and the transfer paper is discharged onto a tray 26 that also serves as a top plate of the image forming apparatus.

Above the array of photoconductors 13Y to 13K,
An optical scanning device 30 is provided. Reference numerals 31 and 32 denote polygon mirrors of the light deflecting means. Reference numerals 33, 34, 3
Reference numerals 5, 36, 37 and 38 denote lenses, and reference numerals m1 to m12 denote mirrors for bending the optical path.

Although not shown, four light sources are provided, and four groups of light beams are emitted from these four light sources. Each group of luminous flux is one or plural depending on whether the optical scanning is performed by the single beam scanning method or the multi-beam scanning method.

Of the four groups of light fluxes, two groups are polygon mirrors 3.
1, and is deflected by the polygon mirror 31 so as to be distributed to the left and right in the drawing, and the photoconductors 13M and 13C are optically scanned. The remaining two groups of light fluxes are the polygon mirror 32.
And is deflected to the left and right in the drawing by the polygon mirror 32, and optical scanning is performed on the photoconductors 13Y and 13K, respectively.

The polygon mirrors 31 and 32 are fixed to the same rotating shaft and integrally driven to rotate, and together with the rotation driving means, constitute "same light deflecting means" for deflecting a plurality of groups of light beams.

The two groups of luminous fluxes deflected by the polygon mirrors 31 and 32 in the area on the right side of the drawing pass through the scanning lens 33 common to these luminous fluxes, and are then separated by the mirrors m1 to m6 to be optically scanned. The light is guided to the photoconductors 13M and 13Y, and the scanning lenses 36 and 3 on the scanned surface side respectively.
5, the light spots are formed on the photoconductors 13M and 13Y to perform optical scanning.

The two groups of light fluxes deflected by the polygon mirrors 31 and 32 in the area on the left side of the drawing pass through the scanning lens 34 common to these light fluxes, and are then separated by the mirrors m7 to m12 to be optically scanned. Photoconductor 13C, 13K
Is guided to the scanning lens 37 on the scanning surface side,
After passing through 38, an optical spot is formed on the photoconductors 13C and 13K to perform optical scanning.

That is, in this optical scanning device, a plurality of groups of luminous fluxes emitted from a plurality of light sources are made into the same optical deflecting means 31, 32.
In the optical scanning device that guides light to different scanned surfaces 13Y to 13K for each group of light fluxes by the scanning and imaging optical system and optically scans a plurality of scanned surfaces, the light fluxes deflected by the optical deflector are Each group transmits at least two scanning lenses while being guided to the corresponding surface to be scanned, and among these scanning lenses, the scanning lens 33 arranged at the position closest to the light deflector is different from each other. The scanning lens 34, which transmits a plurality of groups of light beams toward the scanning surfaces 13Y and 13M and is arranged at a position closest to the light deflector, is different from the surface to be scanned 1.
It transmits a plurality of groups of light fluxes toward 3C and 13K.

The scanning lenses 33 and 34 are arranged at positions closest to the surface to be scanned, with the power in the main scanning direction: Pm and the power in the sub scanning direction: Ps satisfying the condition: Pm> 0 ≧ Ps. The scanning lenses 35 to 38 having a positive power in the sub-scanning direction transmit only a group of light beams directed to the same surface to be scanned (claim 1).

Further, the scanning lenses 33 and 34 are the first type scanning lenses in the invention of claim 5, and the scanning lenses 35 to 38 are the second type scanning lenses in the invention of claim 5, respectively. . When the full-color mode (multi-color mode) is executed with the above-described configuration, the image forming process including the optical scanning is executed for each of the photoconductors 13Y to 13K. Photoreceptor 1 as an example
Image formation for 3Y will be described.
The light beam (which is deflected by the polygon mirror 32) to be optically scanned is modulated by the yellow image information.

The photoconductor 13Y is uniformly charged by the charging means 4Y while rotating at a constant speed in the clockwise direction, is optically scanned by the light flux to write a "yellow image", and an electrostatic latent image (corresponding to the yellow image) is written. A negative latent image) is formed. This electrostatic latent image is developed by the developing device 5Y and visualized as a "yellow toner image". In this way, a yellow toner image is formed on the photoconductor 13Y.

Similarly, a magenta toner image is formed on the photoconductor 13M, a cyan toner image is formed on the photoconductor 13C, and a black toner image is formed on the photoconductor 13K.
The transfer paper S to which the toner images of the respective colors are to be transferred is fed from the cassette 10 and mounted on the conveyor belt 12 by the registration rollers 19 with timing. At this time, the charger 20 discharges toward the transfer sheet S,
The transfer paper S is electrostatically attracted to the conveyor belt 12.

The transfer paper S adsorbed on the conveyor belt 12 is
The yellow toner image is conveyed by the counterclockwise rotation of the conveyor belt, and the transfer charger 6Y transfers the yellow toner image to the photoreceptor 13.
From Y, a magenta toner image is transferred from the photoconductor 13M by the transfer charger 6M, a cyan toner image is transferred from the photoconductor 13C by the transfer charger 6C, and a black toner image is transferred from the photoconductor 13K by the transfer charger 6K. The toner images of the respective colors are superimposed on each other on the transfer paper S to form a color image.

Then, when the separating means 21 removes the electric charge from the transfer sheet S, the transfer sheet S is moved by the strength of the waist of the transfer belt 12 itself.
Then, the color image is fixed by the fixing device 24, and then discharged onto the tray 26 by the discharge roller 25.

After the transfer paper S is separated, the conveyor belt 12 is destaticized by the destaticizing means 22, and the belt cleaner 23 removes toner and paper dust.

[0117]

EXAMPLES Specific examples of the scanning and imaging optical system will be described below. Throughout the examples, a semiconductor laser having an emission wavelength of 780 nm is assumed as the light source. The situation from the light source to the light deflection means is also the same, and the light flux emitted from the light source is coupled by the coupling lens, and the distance from the deflection surface to the natural condensing point is about 1200 m.
It becomes a "weakly focused beam" of m. Depending on the design, a parallel light beam or a divergent light beam may be used.

The light beam transmitted through the coupling lens passes through the aperture for setting the light beam diameter on the surface to be scanned to a desired value, and the cylindrical lens having a power only in the sub-scanning direction causes the light deflecting means to move. A long line image is formed in the main scanning direction in the vicinity of the deflecting / reflecting surface of the polygon mirror.

The light beam reflected by the light deflecting means is guided to the surface to be scanned through the first scanning lens and the second scanning lens which form the scanning imaging optical system. The optical path length from the origin of deflection by the light deflecting means to the surface to be scanned is 175 mm in all the examples. The aperture has a rectangular opening shape,
The opening width is 3.6 mm in the main scanning direction and 0.
It is 22 mm.

Lens data after the cylindrical lens are shown below. Rm and Rs are the radii of curvature in the main scanning direction and the sub-scanning direction, D is the surface spacing, and N is the refractive index at the wavelength used (780 nm). The specific configuration of the optical scanning device may be, for example, the configuration shown in FIG. 1 or 3. The unit of the quantity having the dimension of length is mm.

[0121]   Example 1 Surface number Rm Rs D N Remark 1 ∞ 13.88 3 1.5244 Cylindrical lens 2 ∞ ∞ 25 1 3 ∞ ∞ 33.3 1 Deflector 4 (*) 160.4 ∞ 13.5 1.5244 1st scanning lens 5 (*) -141.3 ∞ 84.2 1 6 (**) -700 -70 3 1.5112 Second scanning lens 7 (***)-700 -15.6 41 1 8 --- Surface to be scanned.

Surfaces marked with (*) (4th and 5th surfaces)
Is a surface having a non-arcuate shape in the main scanning direction and having no power in the sub scanning direction over the entire effective area. The expression of the non-arc shape is as follows: coordinate in the optical axis direction: X, coordinate in the main scanning direction:
Y, high-order coefficient: A4, A6, A8, A10 ... X = Y ² / {Rm + Rm ・ √ {1- (1 + K) Y ² / Rm ² } + A ₄ Y ⁴ + A ₆ Y ⁶ + A ₈ Y ⁸ + A ₁₀ Y ¹⁰ (1) In the above notation, for example, "E-14" means "10 ^-14 ", and this numerical value relates to the numerical value immediately before it.

The surface marked with (**) (sixth surface) is arcuate in the main scanning direction, and the radius of curvature of the sub-scanning section (virtual cross section parallel to the main scanning direction) is the entire effective area. It is constant over. The surface marked with (***) (seventh surface) has an arc shape in the main scanning direction, and the radius of curvature of the sub-scanning section can be expressed by the following equation.
The radius of curvature of the sub-scan section: Rs (Y) changes according to the lens height in the main scanning direction: Y as expressed by the following equation (2). The field curvature in the direction is well corrected. Rs (Y) = Rs + a ₂ Y ² + a ₄ Y ⁴ + a ₆ Y ⁶ (Rs is the radius of curvature at Y = 0) (2) a ₂ = -6.3E-04, a ₄ = a ₆ = 0.

FIG. 4 shows a change in beam diameter with respect to defocus in the main scanning direction (a) and the sub-scanning direction (b) according to the first embodiment. Small diameter (4 in both main and sub scanning directions)
A beam diameter characteristic with a large depth margin is obtained at 0 μm or more).

FIG. 5 shows an aberration diagram. The left side of FIG. 5 shows the field curvature characteristic, the broken line is the main scanning direction, and the solid line is the sub scanning direction. The central figure of FIG. 5 is the "scan line curve characteristic". Further, the diagram on the right side of FIG. 5 is a constant velocity characteristic, the solid line is linearity (magnification error when the evaluation length is infinitely small), and the broken line is (deviation amount from ideal image height / ideal image height) × 100%. is there. The following aberration diagrams also follow this example. In the aberration charts of the examples, the vertical axis represents the image height and the unit is mm, and the horizontal axis in the field curvature and scanning line bending characteristics is also in the unit of mm.

As is apparent from the figure, each aberration is well corrected. Since the power Ps in the sub-scanning direction of the first scanning lens arranged on the side of the light deflector is 0,
The incident height of the light beam in the sub-scanning direction does not affect the aberration, and therefore, using the scanning imaging lens of the first embodiment,
When the optical scanning device of the type shown in FIG. 1 is constructed, the aberrations on different scanned surfaces are completely the same. Therefore,
It is possible to significantly reduce the relative displacement between the scanning surfaces in the main / sub scanning direction.

Example 2 Surface number Rm Rs DN Remark 1 ∞ 13.88 3 1.5244 Cylindrical lens 2 ∞ ∞ 25 1 3 ∞ ∞ 33.3 1 Deflection / reflection surface 4 (*) 160.4 -100 13.5 1.5244 First scanning lens 5 (*)- 141.3 -135 84.2 16 (**) -700 -70 3 1.5112 2nd scanning lens 7 (***) -700 -15.6 41 1 8 --- Surface to be scanned In Example 2, both surfaces of the 1st scanning lens are It is “convex toward the deflecting reflection surface side” in the sub-scan section and has a weak negative power (Ps <0) in the sub-scan direction.

The shapes in the main scanning direction of the surfaces marked with (*) (the fourth surface and the fifth surface) are represented by the above equation (1). The shape in the sub-scanning direction is expressed by the following equation (2).

[0129]

That is, only the fourth surface has a radius of curvature in the sub-scanning direction which changes depending on the lens height in the main scanning direction: Y, whereby the first scanning lens is transmitted according to the surface to be optically scanned. Even if the position of the light beam in the sub-scanning direction is different, it is possible to satisfactorily correct the scanning line curve and reduce the relative scanning position shift in the sub-scanning direction.

The surface marked with (**) (sixth surface) has an arc shape in the main scanning direction, and the radius of curvature of the sub-scan section is constant over the entire effective area. The surface marked with (***) (seventh surface) has an arc shape in the main scanning direction, and the radius of curvature of the sub-scanning section can be expressed by equation (2). The radius of curvature of the sub-scanning section of this surface arbitrarily changes according to the lens height in the main scanning direction, and thus the field curvature in the sub-scanning direction is satisfactorily corrected.

A ₂ = -6.3E-04, a ₄ = a ₆ = 0 Aberration diagrams of the optical system of the second embodiment are shown in FIGS. 6 and 7 following FIG. The aberration diagram of FIG. 6 relates to “a light beam that transmits a position ± 3 mm away from the optical axis in the sub-scanning direction”, and the aberration diagram of FIG. 7 is “± 1 mm in the sub-scanning direction from the optical axis.
FIG. 8 is an aberration diagram regarding “a light beam that transmits a distant position”. At each of these transmission positions, the field curvature in the main and sub-scanning directions is satisfactorily corrected, and especially the scanning line curve is satisfactorily corrected. Further, the difference in the constant velocity characteristics between the light fluxes is small.

Therefore, if the same optical scanning device as shown in FIG. 1 is constructed by using the optical system of the second embodiment, the photoconductors 9A to 9B can be substantially optically scanned in the same good condition. Further, since the first scanning lens has a negative power in the sub-scanning direction, it is easy to separate the light beam between the first and second scanning lenses.

Example 3 Surface number Rm Rs DN Remark 1 ∞ 13.88 3 1.5244 Cylindrical lens 2 ∞ ∞ 25 1 3 ∞ ∞ 33.3 1 Deflection / reflection surface 4 (*) 160.4 -80 13.5 1.5244 First scanning lens 5 (*)- 141.3 -135 84.2 16 (**) -700 -70 3 1.5112 Second scanning lens 7 (***) -700 -15.6 41 1 8 --- Scanned surface The difference between Example 3 and Example 2 , The radius of curvature of the incident side surface of the first scanning lens is the only other data,
The coefficient including the aspherical shape is the same as that of the second embodiment.

Aberration diagrams relating to Example 3 are shown in FIGS. 8 and 9 following FIG. Fig. 8 shows "± in the sub-scanning direction from the optical axis.
FIG. 9 is an aberration diagram regarding “a light beam that transmits a position 3 mm apart”, and FIG. 9 is an aberration diagram regarding “a light beam that transmits a position ± 1 mm away from the optical axis in the sub-scanning direction”.

Although the field curvature, scanning line bending, and constant velocity characteristics are well corrected, the difference due to the light beam transmission position is larger than that in the second embodiment. This is because the negative power in the sub-scanning direction in the first scanning lens: Ps
Due to making it stronger than the one.

Example 4 Surface number Rm Rs DN Remarks 1 ∞ 13.88 3 1.5244 Cylindrical lens 2 ∞ ∞ ∞ 25 1 3 ∞ ∞ 33.3 1 Deflection / reflection surface 4 (*) 160.4 ∞ 13.5 1.5244 First scanning lens 5 (*)- 141.3 ∞ 84.2 16 (**) -700 -70 3 1.5112 Second scanning lens 7 (***) -600 -15.6 41 1 8 --- Scanned surface The difference between Example 4 and Example 1 is that Only the radius of curvature in the main scanning direction of the exit side surface of the second scanning lens is the same, and other data are the same as in Example 1 including the coefficient of the aspherical shape.

FIG. 10 shows an aberration diagram in a manner similar to FIG.

As is clear from the figure, each aberration is well corrected. Since the power Ps in the sub-scanning direction of the first scanning lens arranged on the side of the light deflector is 0, the incident height of the light beam in the sub-scanning direction does not affect the aberration. Therefore, using the scanning imaging lens of Example 4, as shown in FIG.
When an optical scanning device similar to the above is constructed, aberrations on different scanned surfaces are completely the same. Therefore, the relative displacement between the scanning surfaces in the main / sub scanning direction can be significantly reduced.

Example 5 Surface number Rm Rs DN Remark 1 ∞ 13.88 3 1.5244 Cylindrical lens 2 ∞ ∞ 25 1 3 ∞ ∞ 33.3 1 Deflection surface 4 (*) 160.4 ∞ 13.5 1.5244 First scanning lens 5 (*) -141.3 ∞ 84.2 16 (**) -700 -70 3 1.5112 Second scanning lens 7 (***) -520 -15.6 41 1 8 --- Scanned surface The difference between Example 5 and Example 1 is in the second scanning. Only the radius of curvature of the exit side surface of the lens in the main scanning direction, and other data are the same as those of the first embodiment including the coefficient of the aspherical shape.

FIG. 11 shows an aberration diagram in a manner similar to FIG.

As is clear from the figure, each aberration is well corrected. Since the power Ps in the sub-scanning direction of the first scanning lens arranged on the side of the light deflector is 0, the incident height of the light beam in the sub-scanning direction does not affect the aberration. Therefore, using the scanning imaging lens of Example 4, as shown in FIG.
When such an optical scanning device is constructed, the aberrations on different scanned surfaces are completely the same. Therefore, the relative displacement between the scanning surfaces in the main / sub scanning direction can be significantly reduced.

Conditions in Examples 1 to 5: 1 to 4
The relationship with is as follows.

The relationship between the conditions of the claims and the embodiment is as follows.

Example 1 Example 2 Example 3 Example 4 Example 5 Condition 1 Applicable Applicable Applicable Applicable Applicable Applicable Condition: 2 Applicable Not Applicable Applicable Applicable Condition: 2 Left side value 0 0.45 0.89 0 0 Condition: 3 Applicable Applicable Applicable Applicable Applicable Condition: 3 Value on the left side 0 0 0 0.04 0.09 Condition: 4 Applicable Applicable Applicable Applicable | β | 0.316 0.311 0.3 0.316 0.316 In addition, among Examples 1 to 5, Examples 1, 4 and 5 are:
It corresponds to the scanning and imaging optical system according to claim 8. Therefore, the optical systems of Embodiments 1, 4 and 5 are "lights for performing optical scanning by deflecting a single group of light beams emitted from the light source by the light deflecting means and guiding the light beams to the surface to be scanned by the scanning imaging optical system. Scanning device "
Can be suitably used as the scanning and imaging optical system in.

Under the above condition 1, the upper limit of Pm is determined by the individual characteristics in the main scanning direction required for the scanning imaging optical system. Further, the lower limit of Ps is determined according to how much the scanning line curve can be corrected.

In any of Examples 1 to 5 described above, the lens surface on the incident side of the scanning lens closest to the light deflector has a shape convex toward the light deflector, and the scanning lens closest to the surface to be scanned. Is "curved in the main scanning direction".

[0148]

As described above, according to the present invention, a novel optical scanning device and image forming apparatus can be realized.
In the optical scanning device according to any one of claims 1 to 7, since the scanning lens through which a plurality of light beams traveling toward different scan surfaces do not have positive power in the sub-scanning direction, light beam separation is easy, and therefore, Since a plurality of light beams can be densely arranged in the sub-scanning direction on the deflecting / reflecting surface of the light deflecting means, the deflecting / reflecting surface of the light deflecting means can be made small, and the light deflecting means can be reduced in size and weight, so that the cost can be reduced. Low noise, high durability,
Low power consumption is possible.

In the optical scanning device according to the eighth aspect, the power of the scanning lens on the optical deflecting means side in the scanning image forming optical system is 0.
Since the shape in the main scanning cross section does not change in the sub scanning direction, even if this lens is displaced in the sub scanning direction, the constant velocity characteristic does not deteriorate and the imaging performance in the main scanning direction does not deteriorate. Further, even if there is a local defect such as a foreign substance in the scanning lens near the optical deflector, since there is no optical axis in the sub-scanning direction, the best sub-scanning position is selected and the scanning lens is arranged. It is possible.

Therefore, the image forming apparatus of the present invention using such an optical scanning device can form an excellent image.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of an optical scanning device and an image forming apparatus.

FIG. 2 is a diagram for explaining conditions: 1 and 4;

FIG. 3 is a diagram for explaining another embodiment of the image forming apparatus.

FIG. 4 is a diagram showing a change in light flux diameter with respect to defocus in the first embodiment.

FIG. 5 is an aberration diagram for Example 1.

FIG. 6 is an aberration diagram for Example 2.

FIG. 7 is an aberration diagram for Example 2.

FIG. 8 is an aberration diagram for Example 3.

FIG. 9 is an aberration diagram for Example 3.

FIG. 10 is an aberration diagram for Example 4.

FIG. 11 is an aberration diagram for Example 5.

[Explanation of symbols]

5 Light deflection means 7 First scanning lens 8A to 8D Second scanning lens 9A-9D Photoconductive photoconductor

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Claims (9)

[Claims] 1. A plurality of groups of light beams emitted from a plurality of light sources are deflected by the same light deflecting means, and are guided by a scanning imaging optical system to a different surface to be scanned for each group of a plurality of light beams to be scanned. In an optical scanning device that optically scans a surface, each group of light beams deflected by an optical deflecting unit passes through at least two scanning lenses while being guided to a corresponding surface to be scanned, and among these scanning lenses, The scanning lens arranged at the position closest to the light deflector transmits a plurality of groups of light beams directed to different surfaces to be scanned, and the power in the main scanning direction: Pm and the power in the sub scanning direction: Ps are Condition: Pm> 0 ≧ Ps (Condition: 1) is satisfied, and the scanning lens disposed closest to the surface to be scanned has a positive power in the sub-scanning direction and a light beam directed to the same surface to be scanned. Is characterized in that only the group of Optical scanning device. 2. The optical scanning device according to claim 1, further comprising: a scanning lens disposed at a position closest to the optical deflector.
The radius of curvature of the incident side surface in the sub-scanning direction: Rs1, the radius of curvature of the exit side surface in the sub-scanning direction: Rs2, the optical path length from the origin of deflection of the light deflecting means to the surface to be scanned: L, the condition is: | (1 / Rs1 ) + (1 / Rs2) | L <0.5 (condition: 2) 3. The optical scanning device according to claim 1, wherein a radius of curvature in the main scanning direction of the incident side surface of the scanning lens disposed at a position closest to the surface to be scanned: Rm1, main scanning of the exit side surface. Radius of curvature in the direction: Rm2, optical path length from the origin of deflection of the optical deflecting means to the surface to be scanned: L is: | (1 / Rm1) + (1 / Rm2) | .L <0.1 (Condition: An optical scanning device satisfying 3). 4. The optical scanning device according to any one of claims 1 to 3, wherein a plurality of groups of luminous fluxes deflected by the optical deflecting means are arranged on the optical deflecting means side and are positive only in the main scanning direction. Scanning lens that has a power of, and that transmits a plurality of light fluxes that are guided to different scanned surfaces, and a scanning lens that is arranged on the scanned surface side and has positive power in the sub-scanning direction An optical scanning device characterized in that light is guided to a surface to be scanned only by two scanning lenses including a scanning lens which transmits a group of light fluxes which are directed. 5. A plurality of groups of light beams emitted from a plurality of light sources are deflected by the same light deflecting means, and are guided by a scanning and imaging optical system to a different surface to be scanned for each group of the plurality of light beams to be scanned. In an optical scanning device that optically scans a surface, a scanning and imaging optical system that guides each group of light beams deflected by an optical deflector to a surface to be scanned has a power in the main scanning direction: Pm, a power in the sub scanning direction: Ps
Satisfies the condition Pm> 0 ≧ Ps (condition: 1), and has the same positive power in the sub-scanning direction as the first type of scanning lens that transmits a plurality of groups of light beams directed to different surfaces to be scanned. A second type scanning lens that transmits a group of light beams directed to the surface to be scanned, and all the scanning lenses arranged on the optical path from the light deflecting means to each surface to be scanned are the first And an optical scanning device which is any one of a second type scanning lens. 6. The optical scanning device according to claim 5, wherein, in the first type scanning lens, the radius of curvature of the incident side surface in the sub-scanning direction: Rs1, the radius of curvature of the exit side surface in the sub-scanning direction:
Rs2, the optical path length L from the starting point of deflection of the light deflecting means to the surface to be scanned satisfies the condition: | (1 / Rs1) + (1 / Rs2) | .L <0.5 (condition: 2) An optical scanning device characterized by the above. 7. The optical scanning device according to claim 5 or 6, wherein in the second type scanning lens, the radius of curvature of the incident side surface in the main scanning direction: Rm1, the radius of curvature of the exit side surface in the main scanning direction:
Rm2, the optical path length L from the starting point of deflection of the light deflecting means to the surface to be scanned satisfies the condition: | (1 / Rm1) + (1 / Rm2) | L <0.1 (condition: 3) An optical scanning device characterized by the above. 8. An optical scanning device for deflecting light flux of a single group emitted from a light source by a light deflecting means and guiding the light to a surface to be scanned by a scanning and imaging optical system to perform optical scanning. Is composed of two scanning lenses, the scanning lens on the side of the optical deflector is a lens having power only in the main scanning direction, and the curvature radius in the main scanning direction of the incident side surface of the scanning lens on the surface to be scanned: Rm1, Radius of curvature in the main scanning direction on the exit side: R
m2, the optical path length L from the origin of deflection of the light deflecting means to the surface to be scanned satisfies the condition: | (1 / Rm1) + (1 / Rm2) | L <0.1 (condition: 3) An optical scanning device characterized by the above. 9. An image forming apparatus for forming an image by performing optical scanning on one or more photosensitive media, wherein the optical scanning apparatus according to any one of claims 1 to 8 is used. apparatus.